The present invention relates to data storage systems. In particular, the present invention relates to glide heads used to detect defects on surfaces of memory discs, such as those used in disc drive data storage systems.
In data processing systems, disc drives are often used as direct access storage devices. In such devices, read/write heads are used to write data on or read data from an adjacently rotating hard or flexible disc. To prevent damage to either the disc or the read/write head, it has been recognized that the surface of the disc should be very flat and free of any bumps or the like which might be contacted by the read/write head. Also, the read/write heads are typically designed to fly over the surface of the rotating disc with a small fly height which is maintained by a film of air (air bearing). During its flight, the head undergoes continuous vibration, pitch, and roll as the topography of the disc changes beneath the head. If the quality of the disc or the read/write head is poor, occasional rubbing or sharp contact may occur between the disc and the read/write head. Such contact may damage the head or the disc, cause loss of valuable data, or all of these.
To ensure that only discs having sufficiently flat surfaces are used in production disc drives, discs are production tested in a quality control procedure prior to installation in a disc drive. Smoothness or flatness testing is performed with a xe2x80x9cglide testxe2x80x9d, which involves flying an air bearing xe2x80x9cglidexe2x80x9d slider over the disc. The glide slider includes a piezo-electric element or other vibration sensor, which may be bonded on the back of the air bearing slider. The vibration sensor detects xe2x80x9chead-disc interferencesxe2x80x9d or xe2x80x9chitsxe2x80x9d. Each instance of vibration is sensed and recorded for either remedial action or toward rejection of the disc. Vibration may be caused by bumps which decrease the clearance of the slider. If a bump is sufficiently large to create eddy currents and swirls in the air stream which cause the glide slider to vibrate, then the bump is recorded as a defect. The glide slider usually flies at a height lower than the read/write head during normal conditions in order to ensure that any asperity high enough to contact the read/write head will be detected.
Many glide slider designs include an inside rail and an outside rail separated by a central cavity. The rails generate a positive pressure lift force for the slider. Since both the inside rail and outside rail create lift, it is important that as the slider moves laterally across the rotating surface of the disc, both the inside rail and the outside rail remain over the surface of the disc. If the outside rail is moved beyond the outer circumference of the disc, the slider will lose its lift under the outside rail and will roll, causing the slider to contact the disc. Generally, the inside rail and the outside rail fly at the same height from the disc surface. This makes it difficult to determine which rail is detecting defects. Hence, when the slider is at the outer circumference and the active rail (rail that is detecting defects) is unknown, roll could occur causing the slider to contact the disc if the outside rail is moved beyond the outer circumference of the disc.
One glide slider design for testing the outermost portion of the surface of a disc without losing lift is described in U.S. Pat. No. 5,963,396 entitled xe2x80x9cGLIDE HEAD WITH AN OUTSIDE ACTIVE RAILxe2x80x9d. The glide slider described in U.S. Pat. No. 5,963,396 employs an outside rail that is longer than the inside rail, with the trailing edge of the outside rail extending beyond the trailing edge of the inside rail. When the slider is used for disc surface testing, the trailing edge of the outside rail is closer to the surface of the disc because of the slope of the glide slider""s flight. Even though this technique is successful in making the outside rail the active rail, the use of rails of different lengths results in uneven lift during slider flight, thereby requiring additional design adjustments to provide slider flight stability.
The present invention addresses these problems, and offers other advantages over the prior art.
A glide head for detecting asperities on a disc surface is provided. The glide head includes a glide slider which includes a glide slider body that has a leading edge, a trailing edge, and a bottom surface therebetween. The bottom surface is centered along a longitudinal axis that extends between the leading and trailing edges. An inside rail is disposed on the bottom surface on a first side of the longitudinal axis and extends from the leading edge to the trailing edge. An outside rail is disposed on the bottom surface on a second side of the longitudinal axis. The outside rail extends from the leading edge to the trailing edge. The inside and outside rails are substantially equidistant from the longitudinal axis at the bottom surface. The outside rail is positioned lower than the inside rail such that a bottom surface of the outside rail extends further from a point on the longitudinal axis on the trailing edge than does a bottom surface of the inside rail.
These and various other features as well as advantages which characterize the present invention will be apparent upon reading of the following detailed description and review of the associated drawings.